1. Field of the Invention
This invention relates to a plug cap for an ignition plug which is used for connecting an ignition cable to an ignition plug in an engine, for example, of an automobile, and more particularly to an improved ignition plug cap in which the provision of a rain cover for preventing rain water from intruding into an ignition plug-mounting hole and an insulating pipe is omitted, thereby reducing a manufacturing cost, and also enhancing an assembling efficiency, and besides a variation in the angle of extending of the ignition cable from the insulating pipe can be prevented.
2. Related Art
A plug cap has heretofore been used for connecting an ignition cable to an ignition plug in an engine. One example of such ignition plug cap will be described with reference to FIG. 8. An ignition plug 3 is mounted in a bottom of an ignition plug-mounting hole 2 formed in an engine head 1. A plug cap 5 is used to connect an ignition cable 4 (which supplies a high-voltage current) to the ignition plug 3.
The plug cap 5 includes a narrow, elongate insulating pipe 6 inserted in the ignition plug-mounting hole 2, the insulating pipe 6 being molded of an insulative resin material. A front end portion of the ignition cable 4, as well as a connection terminal 7 for connecting the ignition cable 4 to an end metal member of the ignition plug 3, is received within the insulating pipe 6. An end cap 8, molded of an insulative rubber material, is attached to a lower end of the insulating pipe 6, and this end cap 8 is fitted on an insulator portion of the ignition plug 3 so as to prevent the leakage of a high-voltage current.
A rain cover 10 for preventing rain water from intruding into the insulating pipe 6 is attached to an upper end of the insulating pipe 6. A flange 12 and an intimate-contact portion 13 of a generally cylindrical shape are molded integrally with a cylindrical body portion 11 of the rain cover 10 fitted on the insulating pipe 6. The flange 12 is held in intimate contact with the surface of the engine head 1 to cover an open portion of the ignition plug-mounting hole 2, and the intimate-contact portion 13 is intimately fitted on the ignition cable 4.
Vent holes 14 and 15, which communicate a space in the ignition plug-mounting hole 2 with the exterior of the engine, are formed respectively in the insulating pipe 6 and the rain cover 10, and extend parallel to the axis of the insulating pipe 6. The vent hole 15, formed in the rain cover 6, is open to a distal end of a conical rainproof portion 16 formed upright on an upper surface of the rain cover 10.
The rain cover 10 for the ignition plug cap 5 tends to become large in size because of its construction. And besides, the rain cover 10 must maintain an insulating effect and a liquid-tight seal for a long period of time while withstanding heat and vibrations produced by the engine, and therefore a relatively expensive rubber material is used to form the rain cover 10, thus inviting the problem that this cost is high.
The ignition cable 4 must be installed along the surface of the engine head 1 so that it will not interfere with other parts provided around the engine. However, a conductor of the ignition cable 4 is thick so as to suppress a voltage drop to a minimum when supplying a high-voltage current, and besides the ignition cable 4 has a shield mesh wire so as to prevent radio noises from leaking to the exterior, and therefore the ignition cable 4 is complicated in construction, and has high flexural rigidity. Therefore, the rain cover 10, which is made of rubber, and hence has low rigidity, can not accurately regulate the angle of extending of the ignition cable 4 from the insulating pipe 6, so that there occurs a variation in the position of installation of the ignition cable 4.
Furthermore, when the rain cover 10 is fitted on the insulating pipe 6, the rain cover 10 is deformed, and therefore there is a fear that the vent hole 15 is crushed, thus adversely affecting the ventilation. If a droplet exists at the distal end of the rainproof portion 16, this droplet is often drawn into the ignition plug-mounting hole 2 by a breathing action of the ignition plug-mounting hole 2 caused by the heating and cooling of the engine, and in some cases this invites the leakage of the high-voltage current and a combustion failure.
There is a further problem that the efficiency of mounting of the ignition cable 4 on the rain cover 10 and the efficiency of mounting of the rain cover 10 on the insulating pipe 6 are low.